1. Field of the Invention
The present invention relates to a binder resin for an electrostatic image developing toner which is used when an electrostatic latent image formed by an electrophotographic process, an electrostatic recording process or the like is developed with a developer, and also relates to an electrostatic image developing toner produced by kneading and pulverizing the binder resin. Furthermore, the present invention relates to a binder resin liquid dispersion for an electrostatic image developing toner, produced from the binder resin, and an electrostatic image developing toner produced by using the binder resin liquid dispersion. In addition, the present invention relates to an electrostatic image developer using the electrostatic image developing toner, and an image forming method.
2. Description of the Related Art
With rapid spread of digitization technology, high image quality is currently demanded for the output such as print and copy by users at the home or office or in the publishing field. Meanwhile, demands for low energy and energy saving in corporate activities and activity result products are increasing so as to realize a sustainable society. To keep up with this trend, also in the image forming method by an electrophotographic process, an electrostatic recording process or the like, electric power saving in the fixing step which involves a large energy consumption, or implementation of an activity with a low environmental load in the step of producing a product by using the obtained material is required. Examples of the countermeasure for the former include more reduction in the toner fixing temperature. When the toner fixing temperature is lowered, in addition to power saving, the waiting time until the fixing member surface reaches the fixing possible temperature after turning on the power source, so-called warm-up time, can be shortened and the life of the fixing member can be prolonged.
Incidentally, as for the binder resin of a toner, a vinyl-based polymer has been heretofore widely used and for obtaining a non-offset property, use of a polymer having a high molecular weight has been proposed. However, a vinyl-based polymer having a high molecular weight has a high softening point and the temperature of a heat roller must be set high so as to obtain a fixed image with excellent glossiness, but this results in reverse movement against energy saving. Furthermore, a toner using a vinyl-based polymer is liable to be attacked by the plasticizer of a plasticized vinyl chloride and has a problem that on coming into contact with the plasticizer, the toner itself is plasticized to bear tackiness and contaminate the plasticized vinyl chloride product (hereinafter referred to a “vinyl chloride resistance property”).
On the other hand, a polyester resin has an excellent vinyl chloride resistance property, and a polyester resin having a low molecular weight can be relatively easily produced. Furthermore, a toner having blended therein a polyester resin as the binder resin is advantageous in that when the toner is melted, good wetting to a support such as transfer paper is exhibited as compared with a toner having blended therein a vinyl-based polymer as the binder resin, and sufficient fixing can be performed at a lower temperature as compared with a case using a vinyl-based polymer having a nearly equal softening point. Therefore, a polyester resin is being used as the binder resin for an energy-saving toner in many cases.
Also in JP-A-4-242752, a polyester obtained from a terephthalic acid/a bisphenol A-ethylene oxide adduct/a cyclohexanedimethanol and having, for example, a number average molecular weight of 3,000 to 3,600, a weight average molecular weight of 8,700 to 9,500, a softening point of 100 to 125° C. and a glass transition point of 55 to 68° C., is used as the binder resin. This polyester is excellent in the production stability and fixing strength by virtue of high strength attributable to the property of the raw material but is disadvantageously very poor in the pulverization property at the production of a toner.
In this way, a non-crystalline polyester resin obtained by polycondensing mainly an aromatic polyvalent carboxylic acid (e.g., terephthalic acid, isophthalic acid), an aliphatic unsaturated carboxylic acid (e.g., fumaric acid, maleic acid), a diol having a bisphenol structure, and an alicyclic diol (e.g., aliphatic diol, cyclohexanedimethanol) has been conventionally used as the polyester binder resin and a large number of patents have been proposed. Also, studies on an alicyclic dicarboxylic acid such as cyclohexanedicarboxylic acid are being made.
For example, in JP-A-56-1952 and JP-A-58-17452, an electrophotographic toner composition using a polyester resin has been proposed, in which the polyester resin is obtained by atmospheric pressure polymerization from a cyclohexene-dicarboxylic acid (cyclohexylene dicarboxylic acid) anhydride or cyclohexanedicarboxylic acid anhydride as the polyvalent carboxylic acid component and a polyhydric alcohol having a bisphenol structure. An object of such an invention is to elevate the glass transition point of a polyester resin and improve the storage stability of the toner, but in this production process, when an alicyclic polyvalent carboxylic acid is used, the molecular weight can be hardly increased by the atmospheric pressure polymerization and since only a resin having a low molecular weight can be obtained, the storage stability is sometimes impaired after all.
In JP-A-10-78679, an electrostatic image developing toner has been proposed, which is characterized by comprising, as the main constituent component, a polyester resin having a glass transition point of 50° C. or more obtained by the polycondensation of a polyvalent carboxylic acid containing 5% or more of a cyclohexanedicarboxylic acid, and a polyhydric alcohol mainly comprising an aliphatic diol or an alicyclic diol and having an aromatic polyhydric alcohol content of 5 mol % or less. It is stated that by this combination, an offset phenomenon at the heat fixing can be avoided and a high-grade image can be obtained.
Similarly, in JP-A-10-130380, for the purpose of improving the transparency, a polyester resin comprising a hydrogenated bisphenol in which the polyhydric alcohol has at least a cyclohexane structure has been proposed.
Also, in JP-A-2004-217721, for the purpose of enhancing the hydrolysis resistance, a polyester having a certain intrinsic viscosity and a certain acid value at the polymer terminal is disclosed, in which out of the constituent components of the polyester, the dicarboxylic acid component comprises an alicyclic dicarboxylic acid component as the main component, and the diol component comprises from 80 to 99.95 mol % of an alicyclic diol component and from 0.05 to 20 mol % of an alkylene diol component having a carbon number of 2 to 10.
In this way, studies on the polymerization components as raw materials of a polyester binder resin are continuing with an attempt to enhance the toner properties, but the polyester binder resin has an inherent problem that the fine line reproducibility is poor. This problem is considered to be attributable to the catalyst contained in the binder resin. Furthermore, the above-described resins all are produced by a production process usually requiring a high energy. In a general polycondensation process, a reaction over 10 hours or more with stirring by a great power under highly reduced pressure at a high temperature exceeding 200° C. is necessary and a large energy consumption is incurred. Accordingly, a huge facility investment is required in many cases so as to obtain durability of the reaction facility.
On the other hand, studies for shifting the production process of a polyester resin from a large energy consumption type to a low energy consumption type have been also reported. For example, in JP-A-2003-55302 and JP-A-2003-261662, an in-water dehydration reaction process or polycondensation process comprising performing a dehydration reaction in water in the presence of a surfactant is disclosed. Also, in JP-A-11-313692, a process for producing a polyester by using an enzyme catalyst is disclosed and for example, a reaction of a sebacic acid and a butanediol at 60° C. in an argon atmosphere is described. In JP-A-2003-306535, synthesis of a polyester by using a scandium triflate catalyst is reported and polycondensation of a butanediol and a succinic acid at 160 to 200° C. which is lower than the conventional polyester polycondensation temperature of 200 to 240° C., is described.
However, there is not known a synthesis example of a non-crystalline polyester by such low-temperature polycondensation. For example, in Polymer Journal, Vol. 35, No. 4, pp. 359-363 (2003), it is reported that a decanediol and an isophthalic acid or terephthalic acid, or bisphenol A and a sebacic acid were reacted at 70° C. in water in the presence of a dodecyl-benzenesulfonic acid catalyst, but the reaction did not proceed. Similarly, in Science, Vol. 290, 10, pp. 1140-1142 (2000), it is reported that with respect to polycondensation at room temperature by using hafnium chloride as the catalyst, polycondensation using a special aromatic diol monomer was performed successfully but the reaction of a general-purpose aromatic dicarboxylic acid monomer and an aromatic diol monomer did not proceed.
Such a failure in the synthesis of a non-crystalline polyester by low-temperature polycondensation is considered to result because monomers constituting a non-crystalline polyester have low reactivity and a reaction thereof does not satisfactorily proceed under the above-described low energy condition.